ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle, Metallic
Splintery, UnevenArthur Thomas, Difficult, Fibrous
BeAlSiO 4(OH)Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
NaAlSi 2O 6Ulrich Henn and Claudio C.